The present invention relates generally to a conveyor, and more particularly for a conveyor for transporting workpieces through heat-exchange zones, that is heating and/or cooling zones.
Conveyors for transporting metallic workpieces through warming ovens or cooling arrangements are already known. For example, German Patent No. 1,269,151 describes a conveyor which is particularly intended for transporting metallic workpieces through a warming oven. The supporting structure of the conveyor is surrounded by thermally insulating means and is cooled. At the center, and the upper portion of each supporting structure, there is provided a longitudinally extending gap through which lifting members are pushed upwardly and outwardly and subsequently retracted again into the thermally protected interior of the supporting structure. In so doing, they lift the workpieces which rest on the supporting structure, upwardly, advance them forward in transport direction, and deposit them again on the supporting structure.
The desired movement of the workpieces requires that the interior of the supporting structure, the lifting members are connected to form a continuous chain, and each lifting member is supported by four rollers which, seen in the transport direction, are spaced at equal distances. These rollers roll on tracks having periodically repeated depressions and crests, the periodicity being equal to the spacing between the rollers.
This and analogous prior-art constructions does not permit the lifting members to perform vertical movements, since the rollers must travel on inclined guide surfaces. This means that at the time the workpieces are engaged for lifting by the lifting members, they are not immediately lifted off the support structure but are first pushed by a certain distance on the same before they are lifted out of contact. Also, when the rollers begin to roll down into a depression and the lifting members therefore begin to descend to deposit the workpieces on the support structure, the roller chain and the chain of lifting elements must be braked. Because of the unavoidable play in these chains, such braking leads to jolting of the chains and the supporting structure.
Moreover, in the prior art using this general type of construction, the rollers must be spaced from one another in the transport direction by quite small distances, in order to maintain the bending stresses acting upon the rollers and the lifting members, as small as possible. Small spacing between the rollers, however, requires very significant inclinations in the ascending and descending portions of the guide tracks on which the rollers move, and this in turn requires that the chains be subjected to strong tensile forces in order to be able to advance them. This means a strong and hence expensive construction.